A method for collecting duodenal juice containing bile under an endoscope is provided. In the method, an endoscope is inserted into a duodenum of a subject from which collection of duodenal juice is performed. In a state in which an illuminating section of the endoscope is stopped at the duodenum, an illumination light is generated. The illumination light has a specific wavelength band capable of displaying a component including bile in an enhanced manner, within a visible wavelength region. By an imaging section of the endoscope, a subject image is captured. The subject image is illuminated by the illumination light of the specific wavelength band. Based on an output signal from the imaging section, a subject information image expressing subject information is displayed in a display section. In the displayed subject information image, duodenal juice containing bile is displayed in an enhanced manner. Then, the duodenal juice is collected.
